Yep, it is called a Google search.
I'm sure many if not all of us have tried using Google to find propane, but still, people often ask how to find propane. So Google isn't cutting it. And as someone noted, many of the results are for residential propane delivery, and Google is even less useful if you need a place that can fill an onboard tank.
Then again, the sites that actually claim to list propane places aren't all that great. I used to use an alternative fuels website that had propane locations
with prices, including the date the price was updated (like Gas Buddy does); it had a "comments" section and when I put in a price, I'd note whether the location could fill onboard tanks on a motorhome. This would have been a GREAT site for RVers, but it had very little participation, even though I'd give a link to the site whenever I was posting about propane.
One thing worth noting--the OP mentioned Menard's (home improvement chain in the midwest). Some Menard's locations do self-service cylinder exchanges (like Blue Rhino or Amerigas), and some do propane fills (none of them do both).
However, if you're at a Menard's that does fills instead of cylinder exchanges, be aware that they charge a flat fee regardless of how much propane they put in, and they don't fill them all the way--they put 18.5 pounds in a tank that can hold 20 pounds. They put in more than Blue Rhino and Amerigas do on their propane exchanges (those have 15 pounds), but it's still not full. But if you're filling a tank on a motorhome, they charge by the gallon for however much they put in.
At the Menard's I went to not long ago, if you were filling an onboard propane tank, you paid $3.45/gallon. If you filled a dead empty 20-pound cylinder, it worked out to $4.36/gallon (and this would be even higher if there was any propane remaining in the tank).
That's one good thing I can say about Tractor Supply--I have yet to encounter one that fills cylinders for a flat fee. And since they have nothing to gain by not filling them all the way, you'll get a full tank, which means it'll last longer before needing to be refilled.
I've filled the onboard tank on my 40-foot motorhome quite a few times at Tractor Supply locations across the country. I always assume I'm going to have to unhook my toad, and sometimes do it before I even try to negotiate the Tractor Supply parking lot. I filled at a Love's not long ago, and was thrilled that I didn't have to unhook the toad--it felt like real luxury.